In recent years there has been an increased awareness that underground storage and distribution systems for hazardous fluids such as hydrocarbon fuels and a diversity of other chemicals need to be improved to prevent from leaking into the environment and potentially contaminating underground drinking water. Both public health and fire safety regulatory bodies have imposed strict guidelines and regulations on such systems to insure public safety.
Leaking underground storage tanks and their associated underground piping systems have become the focus of the Federal Environmental Protection Agency (EPA) to initiate federal and state legislation that would require an improved means of storage, distribution, leak detection and accounting for all stored fluids which are deemed to be hazardous. The EPA has conducted studies which show that underground piping failures are caused by poor installation practices. Corrosion and structural failure are responsible for most of the leaks reported.
In response to this public awareness and concern, equipment specifiers and manufacturers have developed improved piping systems in recent years to provide a greater degree of protection for the environment. Most of these improved piping systems provide a second barrier of protection around the primary fluid supply piping, commonly referred to as "secondary containment".
For purpose of this description, underground piping systems are defined as the means of transferring liquids from a buried underground storage tank, using the tank's electrically powered dispensing pump to a generally metered dispensing unit or dispenser, generally located above ground. An underground piping system which is secondarily contained by a larger diameter piping system is generally referred to as a double-wall piping system. The primary distribution pipe which is contained is commonly referred to as the supply pipe and the larger outer secondary containment pipe is commonly referred to as the containment jacket or pipe. Other secondary containment components such as surface access chambers that are installed around the tank's pump and underneath a dispenser, are commonly referred to as access sumps. These storage, transferring and dispensing systems are typically found at service stations which market gasoline and diesel fuel. These pipes are also known as double wall pipes.
Equipment manufacturers have in recent years introduced supply piping systems and/or secondary containment systems for these supply piping systems of various designs and material selections. The following double wall piping systems are considered to be prior art to the present invention.
A secondary contained underground piping system has been proposed which features a non-flexible fiberglass supply pipe system fully contained by a larger non-flexible fiberglass containment piping system.
Another secondary contained underground piping system features a non-flexible fiberglass or steel supply pipe fully contained by a combination of both a larger flexible and non-flexible polyethylene telescoping containment pipe. The telescoping containment pipe design permits the complete inspection of the supply pipe line during assembly and integrity testing.
Alternatively, one can employ a secondarily contained underground piping system which features a non-flexible fiberglass or steel supply pipe fully contained by a larger non-flexible polyethylene telescoping containment pipe. The containment components of these systems are generally joined by means of metal fasteners and flexible seals. Yet another secondarily contained underground piping system features a fiberglass or steel non-flexible supply pipe partially contained by a flexible membrane piping trench liner.
Other systems include a secondarily contained underground piping system which features a fiberglass steel non-flexible supply pipe partially contained by a non-flexible fiberglass trench liner or one which features a flexible nylon composite supply pipe fully contained by a larger flexible polyethylene containment pipe.
It has also been proposed to have a secondarily contained underground piping system which features a flexible rubber composite supply pipe fully contained by a larger flexible polyurethane composite containment pipe. The flexible supply pipe is made of a rubber or elastomeric material for flexibility and requires metallic couplings installed on each end of a pipe section for attachment to a metallic short bend radius tee or elbow supply fitting. The flexible containment pipe is a thick wall tube which provides structural strength but limited flexibility.
The introduction of continuous flexible supply pipe a number of years ago was a means of reducing the amount of connection joints in the supply pipe compared to the commonly used steel and fiberglass non-flexible supply piping systems. The first flexible supply pipe which was introduced was a non-contained thin walled flexible copper tubing which was directionally bent to accommodate the routing required to connect the tanks pump to the various dispenser. The second flexible supply piping system was introduced in Europe, which was a direct burial or non-contained flexible polyethylene tubing which had thick wall and offered only a limited amount of flexibility. Both of these flexible supply piping systems did not require the use of access sumps. The third flexible supply piping was introduced several years ago and was secondarily contained a flexible containment pipe inside and did require the use of access sumps.
Some notable advantages of flexible double wall piping systems include considerably fewer piping joints than conventional double wall piping systems and also provide the unique feature of removing the supply pipe, in the event of a problem, without the need for excavation. These systems feature continuous lengths of both flexible supply pipe and flexible containment pipe which are made available in rolls of very long lengths. From these long lengths, pipe sections may be custom cut to length for installation between two or more surface access sumps. This feature eliminates the need for any directional fittings in the flexible containment pipe line, thus eliminating the need of any piping joints between the interconnected access sumps. The flexible primary piping does require the use of directional fittings but these fittings are located within the surface access sumps where they are surface accessible for inspection and maintenance. This piping design permits complete access to and observation of all the primary and secondary piping joints from the ground surface without the need for excavation.
There are also some notable disadvantages of both of these flexible double wall piping systems. Thin walled corrugated flexible containment pipe is easy to damage and difficult to repair. The inner corrugations restrict fluid migration from the source of the leak to the collection sump. The thin polyethylene material will not meet the Underwriters Laboratory standards for secondary containment. Thick walled non-corrugated flexible containment pipe requires the use of a soft elastomeric material in order to achieve limited flexibility. It is also questionable as to whether or not this material will meet the UL standard for secondary containment. Inner corrugated flexible supply pipe provides good flexibility but poor hydraulic flow efficiency and a low maximum operating pressure. The internal corrugations cause the pipe to be pressure expandable, which can produce faulty readings for in-line leak detection devices and make it difficult to connect internally expanded coupling devices, which could result in a leak. Thick walled flexible rubber supply pipe is heavy and has a highly resistive outer surface which makes it difficult to install into the flexible containment pipe. Rubber material is an unsatisfactory material to use as a supply pipe and will not likely meet the UL standard for primary containment.
All of the secondary contained piping systems and access sumps discussed above have developed over a relatively short period of time in response to the continuously changing environmental and safety regulations.
Shown in my co-pending application entitled Environmentally Safe Underground Piping Systems, filed Mar. 25, 1992 and bearing Ser. No. 07/857,361, is a double wall piping system that consists of a secondarily contained underground piping system. That system includes a flexible coaxial pipe in which the inner primary supply pipe is integral with the outer secondary containment jacket or pipe. This coaxial construction permits this dual purpose pipe to provide the means of both primary liquid supply and secondary containment within the same pipe. The double wall pipe has an interstitial space between the outer surface of the inner pipe and the inner surface of the outer pipe.
One of the more important features of the piping system described in my co-pending application is the interstitial space between the inner pipe and the outer pipe. This space primarily serves as a secondary containment area, so that leakage from the primary pipe or inner pipe will be contained by the secondary containment jacket or outer pipe. It would be of particular advantage in the art if the space between the two pipes could be used for testing and monitoring the condition of the inner pipe. Accordingly, an object of the present invention is to provide a method and apparatus for testing of the integrity of the inner pipe of a coaxial pipe system.
Similarly, it would be of great advantage if that interstitial space could also be used to test the integrity of the outer jacket or containment pipe. That is an additional object of the invention.
In piping systems which include many segments or sections of pipe, it is necessary to connect these sections in a leakproof manner. One of the difficulties in making these connections is that of providing a connection between the interstitial space of the piping system. It is relatively straightforward to connect the inner pipe using conventional connecting devices and seals. Connecting interstitial regions is more difficult when the junction of the pipes being connected branches in several directions, such as when a tee junction is used to take part of the contents of the inner pipe to a dispenser pump while passing the remainder of the fluid onto the next station. If one can picture the need for a series of double wall pipes to run from a storage tank to a plurality of gas station pumps, it can be appreciated that the connection of the interstitial space is at best geometrically difficult. Accordingly, another object of the present invention is to provide a device for connecting the interstitial space of two coaxial pipes which have been joined to connect the inner pipes to each other.
Often times, the interstitial space is allowed to vent into a sump or other device used to contain the junctions which, of course, have the potential for leakage. Sensors are then placed in the individual sumps so that fluid expelling from the interstitial space will be detected and alarm signalling the presence of a leak will be sounded. However, this leads to additional expense since a separate sensor or alarm system must be provided for each connecting region or sump. Routine inspection to verify that the alarm system is in operation thereby require significant labor as each separate system must be inspected.
Accordingly, it is an object of this invention to provide a simple monitoring system for coaxial pipes which have been connected into a system of multiple pipes which requires only one monitoring unit.
Yet another object of this invention is to provide apparatus and a method for a simple and leak proof way to monitor a system with a plurality of pipe systems and stations.
Other objects will appear hereinafter.